Leiomyoma of the uterus with multiple extrauterine smooth muscle tumors: a case report suggesting multifocal origin.

A 17-year-old woman underwent hysterectomy for removal of a "mitotically active" (six to seven mitoses per 10 high-power fields) yet otherwise benign-appearing cellular smooth muscle tumor. Eleven years later, she developed multiple histologically benign smooth muscle tumors in the posterior mediastinum, deep soft tissues of the neck, paravertebral region, incisional scar, and mesentery. The distribution and histologic appearance of the tumors, as well as the protracted clinical course, suggest multifocal origin rather than widespread metastases from a low-grade uterine leiomyosarcoma. This case raises the possibility that some similar cases reported as so-called benign metastasizing leiomyoma may be more satisfactorily explained by the concept of multifocality.